Apparatus for treating hydrocarbon vapors



w. F. SIMS ET AL 1,918,670

APPARATUS vFOR TREATING HYDROCAREON VAPORS Filed Nov. 23, 1929 2sheets-sheet 1 July 18, 1933.

2 Sheets-Sheet 2 06000 OOOO C0000 .COOOO W. F. SIMS ET AL Filed Nov. 23,1929 ooood oooooo ooooo WBC @wm wb APPARATUS FOR TREATING HYDROCARBON-VAPORS July 18, 1933.

7AM W. 6240' c'lccoww Patented July 18, 1933i UNITED y STATES PATENTOFFICE WILLIS r. sins AND VENUS U. cLonn, or WICHITA rALLsQTEXAs,AssIGNoRs To rANHANnLn REFINING COMPANY, or wrcHrrA FALLS, sEXAs, ACORPORATION or L have method of cracking under vacuum and a 'rnXAsAPPARATUS non TREATING HYnnoeARBoN vArons Application filed November23V, 1929. .Serial No. 409,407.

. fuel from petroleum by the process conimonly known cracking. Thepresent a pplication is a continuation iu part of our prior cmjiendiugapplication filed February 16, 1928, Serial No.72541,753, in which wedescribed and claimed an improi'fed complete, plant for inacticing thene. In the present case we shall describe tue same general system.,together with improved pri ,y mary and cracking stills combined in onestructural unit, as wel] as ('-erlain specilic features and methods ofoperation of thek plant as a while.

Very briefly stated, the invention we pre- Q sent has for its basis thediscoveryou our part that by cracking, fractionating, and

cooling under a vacuum, in whole or in part, we can increase the yieldof a product containing unsaturated connpounds and aromatics whicheminently suitable for motor fuel; and that by suitably regulating thetemperature-s 'and pressures (sub-atmospheric) in different parts of thesystem, we can not only yatly ecouomize heat and thereby econonnze fuel,but we can also pro duce a product containing practically 100% of thedesired unsaturated and aromatic compounds. y

(')ur amiaratus. as it will be described, coinprises a inieheating stillfor the charging stock, a cracking still, preferably preceded by aflashpot into which the oil from the preeae is e: ai er 'i o iz. ai a rh t r \pi id l irt i ipois, rind f1 su( cession of iinerrelatedfractionating towers or dephlegniators with one or more vacuum pumps,heat exch anger, cooler and separator, and an absorption tower, allarranged as will be described in detail hereinafter. In addition to theregulation of pressures in each element of the systfiim, from thepreheater to the separator and absorber, we have found it possible toarrange a graduated heat transfer by means of which make-up oil, orre-V` 'hixed fractions to be crackeiil, take up practically all the heatenergy in the cracked vapors. in a counter cin'rentY progressioiithrough the fractionators. The makesup oil and refluxed fractionsinstead of going direct lo the cracking still. have their tempera ture if ed so that they can be converted into vapors 1n the flashpot, fromwhich the vapors pass, together with those from the primary heater, tothe cracking still. y

By maintaining a vacuum or a sub-atmospheric pressure in the crackingzone (and preferably in the flashpot and frac-tionators), crackingcommences at a lower temperature, while the raising of the absolutetemperature, together with the turbulent and rapid motion ofthe vaporsthrough the cracking tubes due to the pull of the vacuum, causes aconsiderable increase in the amount of heat energy taken up per squarefoot of surface, with a co'rrespomling increase in the amount of crackedproducts.` Vithout limiting ourselvesV to one specific sot of pressures,we have found in actual practice that suitable pressu res for our systemand our method are from l5 to GO pounds on the primary heating still',from 12 to la pounds absolute pressure on the flashpot, and from 6 to 14pounds abso lute (or a higher vacuum) on our cracking zone,fractionating towers, cooler and sepa rater. It is 'to be understoodthat the word vacuum as used in this specification means therefore anypressure below that Iof the` atmosphere7 but the actual pressuresemployed will be stated in pounds absolute.

A particular feature which we shall claim herein is the arrangement of'the absorption tower and its relationto the fractionators whereby thegasoline which is carried olf entrained with the fixed gases from thesepa# rator can be stripped olf, and returned to the last fractionatorfrom which it will go over to the cooler and bereturned to the separatorfor storage. For this purpose the fixed gases are either pumped orconductedl under their own pressure to a point near the bottom oftheabsorption tower, while light gas oil, from the bottom of theVfractionator tower, wither without an intake of make-up Voil which ispreferably also light gas oil, is introduced into the upper part of theabsorp`V tion tower, which tower contains means for lili) in thefractionators to be flashed and recracked without going through theprimary heater. In addition to this direct effect upon the gas oil, itis also used to cool thegvapors in the fractionator into which it ispumped. An important feature of this operation is the heat exchangerbetween the last fractionator and the absorption tower. The oil drawnfrom the bottom ofthe absorption tower, eX- cept for its use asstripper' as aforesaid, is to be directly refluxed as stated. The oildrawn from the absorption tower, which carries with it the gasolinestrippedeff therein, is returned to the upper part of the fractionatorsafter passing through the heat eX- changer and receiving therein heatfrom the oncoming oil from the fractionator. In these respects thesystem is cyclic in its operation, as will further appear from thedetailed description hereinafter. It conserves both gasoline vapors andheat, and permits only Waste gases to be finally discarded.

The details of construction will sufliciently appear from thedescription hereinafter.

Our invention is illustrated in the accompanying drawings, in which Fig.1 is a diagrammatic side elevation With parts in section showing thegeneral arrangement of our apparatus.

Fig. 2 is a vertical transverse section of the preheater and crackingstill taken on the line 2-2 of Fig. 3. y

Fig. 3 is a horizontal longitudinal section of the same, taken on theline 3 3 of Fig. 2.

Referring first to Fig. l, l designates a lashpot receiving the heatedoil through valve 23 and pipe 52 from the pipe still in the furnace 2a.Charging stock is forced into said pipe still through the pipe 53 bypump 54. The oil may enter the fiashpot as vapors already formed, or itmay be superheated oil transformed to vapor in this pot by release frompressure. The vapors from this flashpot passing through pipe 55 to thecracking tubes 56 in the furnace 2, will be at or above the equilibriumboiling point of the oils from which they are produced. This equilibriumboiling point is referred to the temperature of the vapors under suchpressures as that carried onour flashpot. This is a vapor temperatureand not an oil temperature. The oil before entering the Hashpot 1 mustbe at temperature some what above this vapor temperature in order tocontain enough heat to take care of the latent heat of vaporization onentering the lashpot.

The preheating is accomplished in an improved still, one form of whichis shown in Fig. 1 and another form in Figs. 2 and 3. In Fig. l, thepipe still 57 is located inthe furnace chamber 2a supplied with top andbottom flue openings 58-59 into the stack 60, each opening provided witha damper as shown, so that the draft through thev pipe 57 may beregulated. The furnace chamber 2a is provided with burners 6l, presentlyto be described, and the entire structure is connected to the structureof the furnace 2 contain-ing the cracking tubes 56, and main burner 62.rIhe. two chambers 2 and 2a are connected by means of openings 63 sothat the heated gases of combustion from burners 62, after passingthrough and around the cracking tubes 56, will be drawn through thepassages 63 and then enter the stack 60 through either the lower orupper opening 59 or58, according to the adjustment of the dampers. lViththe upper draft 58 open, all the waste heat from the cracking furnace 2passes through and around the preheating tubes 57, and the oil thereinis thus raised to a temperature suitable for flashing and introductionas vapors into the cracking tubes 56.

The burners 61 placed under the primary heating tubes are used inbringing the plant on stream at the beginning of a run. By using theseburners 6l w'e do not have to fire the cracking tubes 56 (by means ofburners 62) so heavily as would otherwise be the case and thetemperature of the oil in the primary tubes is quickly raised to such apoint that vapor is formed when released to the iiashpot l. After theplant is once on stream and the maximum fire is placed under thecracking tubes 56 by burners 62, the burners 6l may be turned down verylow or completely cut out and the temperature of the oil iiowing in theprimary heater may thereafter be regulated by the proper use of thedampers as already stated.

Referring to Figs. 2 and 3, the enclosure 2a is built on the side of themain furnace 2, and they are connected by an arched roof 2z. Thecracking tubes 56 and the preheating tubes 57 are disposed horizontallyand parallel to each. other in the two chambers 2 and 2a, with theirbends lying outside the end fire walls of the respective chambers, andenclosed with thin metal plates 65-66-67- 68. The furnace 2 islengthened out at both ends as shown in 2a' and 2y, these two ends beingarched as indicated in dotted lines 21o in Fig. 2, and constitutingDutch ovens projectingl into which are the burners 62. Burners 6lproject into the furnace 2a be` neath the preheating tubes 57 and allthe burners are fitted with valves. The heated gases and products ofcombustion from the burners 62 are received in the Dutch ovens Qafand2y, and conveyed through the arches 21o into the central chamber 2,passing upwardly therein through and around the cracking tubes 56 andthence being deected by the arch 2z through the passageway 68a into thechamber 2a. If the burners 6l. are in operation at the same time, forpurposes of bringing the plant on stream, then the damper in the upperflue 59 should be open and that in the lower flue 58 should be closed.After the plant is on stream. as already stated, and the maximum fire isplaced under the cracking tubes 56, then burners 61 may be turned downvery low or completely cut out, and by regulating the dampers in fiuepassages 58 59, more or less of the heated gases coming through thepassageway 63a may be deflected downwardly through and around thepreheating tubes 57, and into the stack through the lower flue passage58.

The vapors from flashpot 1 are drawn through the cracking tubes 56preferably at a temperature from 1000o F. to 1200o F., and as alreadystated a pressure of 6 to 14 pounds absolute is maintained on thecracking tubes by vacuum pump 14. Thislow pressure on the vapors causesthe temperature atwhich the cracking reaction takes place to be lowered.It also causes the velocity of the vapors, considering a constantgallonage of raw oil charged, to be higher than in a system operated ator above atmospheric pressure, and this vapor velocity gives a. moreturbulent flow of the vapors in the tubes causing a greater heattransfer per square foot of heating surface. The vacuum pump 14 islocated in such a position, with suitable connections, througli lines30, 39, 40 and 42, and valves 3, el, 5, 19, `416, 20, 21 and 25, thatthe vacuum may be appliedat the discharge from theV tubes in the heatingzone 2 pumping the va-l pors from said tubes to cooling and separationtower 6 or the vacuum may be applied on the separator drum 10 and thevapors removed therefrom discharged into absorption tower 11.

The vapors entering the cooling and separation tower 6 may be at or`below atmospheric pressure, depending on the point at which the vacuumis applied to the system, and will be at an elevated temperature,preferably from 1.000O F. to 1200o F., depending on the temperaturefound most suitable to give the largest practical yield of gasoline orrelated light oils. Because of this elevated temperature of these vaporsthey contain considerable quantities of heat that must be removed beforethe products of the reaction producedfin the tubes can be condensed andmade stable under atmospheric conditions. This heat is removed in twoways: (1) by causing the hot vapors to come in Contact with a downwardiiow of liquid oil, drawn from the bottom of cooling and separationtower 7 by pump 13, and discharged through valve 18 to tower 6,preferably contacted with the hot vapors over a series of baile platesplaced in this tower; and (2) by caus-.

ing the vapors to come in contact with cooling coils 26, 26', 26 and 26placed in this tower, through which oil of relatively lower temperaturethan the vapors is caused to flow by pump 15. This causes the heat to beutilized (1) by vaporizing the incoming oil from tower 7, and (2) by theabsorption of the heat by the cooler oil flowing in the cooling coils.This cooling effect will cause a heavy residue to collect in the bottomof the cooling and separation tower 6 which is re- Y I in this tower iscarried to such a pointthat a large portion of the vapors entering itare caused to condense to liquid. This liquid is drawn from tower 7 bypump 13 which discli-.arges a part of it into tower 6 at 18 and a partthrough the coils 26, 26, 26 and 26". Valves 18 and 47 are so located onthe discharge line from pump 13 that all or any part of the liquid fromthe bottom of the cooling and separating tower 7 may be caused todischarge into either the tower 6 or the ons 26, eef, 2e, 26.

The vapors from the tower 7 enter another tower8 at or below atmosphericpressure depending on the point at which the vacuum is applied to thesystem and in tower 8 they are further cooled and fractionated. Thistower is preferably of the bubble type. Cooling is effected by causingthe vapors to come in contact with the coil 28 through which oil at alower temperature than the vapors Visv caused to fiow by pump 15. Thiscooling allows a considerable portion of the vapors to be condensed andthe condensed fractions are removed from the bottom of the tower throughthe heat exchanger 17 by the pump 15. A part of the oil, after havingbeen cooled by passing through the heat exchanger 17, is discharged bypump 15 through valve 31 into the absorption tower 11, and a part of theoil is discharged through coils 28 and 27, 27 through valve 32. Valves31 and 82 may be so opened or closed as to cause any desired quantity ofoil to flow in either direction.

The vapors in the tower 8 are also cooled by the liquid from the bottomof the absorption tower 11 which is pumped from tower 11 by pump 16through heat exchanger 17 where the temperature of this liquid is raisedby liquid flowing in a counter current from the bottom of tower 8, andit is Vthen discharged into tower 8 through valve 83. The temperature ofthe liquid entering tower 8 may be controlled by passing by the heatexchanger with a portion of the relatively cool liquid from absorber 11.This by-pass may be of any suitable or desired construction, and isshown at in the drawings. The liquid from absorber 1l contains the verylight fractions not condensed by water cooling coil 9. These absorbedlight fractions are removed from this liquid on its entrance into rtower8 due to the heat it gains in heat exchanger 17 and the hot vaporsentering tower 8.

The vapors from the tower 8 are caused to pass. through water coolingcoils 9 where 'they are condensed at atmospheric pressure l() are eitherdrawn Jirom it by vacuum pump lsor are caused to pass into absorbingtower ll by reason of their own pressure. When thus passing into theabsorbing tower by their own pressure,A their path is through pipe 250,through valve 25 (both valves 20 and 2l beine` closed and so to thetower ll throuO-h,

the pipe 30a. This also depends on the point which the vacuum is appliedto the system. These vapors V[low vin a counter-current to the cooledliquid from the bottom of the tower 8 and the lighter gasoline orrelated lighter oils are absorbed in this liquid. The tower ll ispreferably of the bubble type.

The lixed gases pass from the tower 1l through line l70 to theatmosphere, or to burners under the furnace, or to commercial gas lines.

The bottoms from tower S, either .with or without make-up oil, deliveredthrough line El and valve 35, not required as absorption oil in thetower ll, are returned to the sys tem and used vas cooling oil in coils28, 27, 27, 26, 26, 26, wnich are placed in towers 8, 7 and 6. The lineconducting this oil to heat exchanging coils 2S, 27 and 27 has valves 36and 37 so situated that all or any part of this liquid can be caused toflow through them. he heated liquid from coils 26, 26", 26 and 26' isconducted through line22 and through valve 38 to llashpot l where all ora considerable portion of this oil is vaporized. The vapor so producedis retreated in the :furnace 2 by being drawn through the tubes placedin this furnace.

The apparatus described above when op.- erated on vapors 'from petroleumgas oil of approximately 300 B. gravity with a vacuum capable of holdingup a -inchcolumn ot mercury maintained ou the system at the separationdrum valve 29, gave a yield ot 16 to 60 percent of light oils having aNew Navy Gasoline boiling range and 3 to 5 percent ot absorbed lightoils which when separated resembled natural. gasoline `in its boilingrange. This gasoline is high in uny washed v tree oli the heavysaturateds and aromatics containing from 60 to 8() percent unsaturatedcompounds and from l0 to 25 percent of aromatic compounds, and is a verydesirable motor fuel.

By varying the combinations of valves, pumps, direct and reflux feed, itis possible to the same apparatus in various ways and for differentoperations, with different classes of oils. The type of equipment will,of course, also vary with the kind of vapors Linder treatment. Theequipment shown is that used when operating on vapors produced from 28to 256 gravity gas oil derived from petroleum. In this case the heat isremoved in four successive stages, in such a manner as to cause thevapors to condense into four dillerent products, one being the linishedgasoline or related light oil-the desired product for whichthe plant wasdesigned-another product being a heavy residuum, and the two otherproducts being a heavy and a light gas oil respectively, which are usedin the system to maintain the desired temperature on the incolningvapors, and as an absorbing oil to remove the very light gasoline likematerial, that is entrained in the gas from the separator drum.

Tn operation, the l'irst tower 6 is used largely as a heat exchanger.The surface otithe' coils 26, 26, 26, 26 should be such as to transferenough of the heat contained in the vapors to the charging oil so thatthe vapors leaving this tower will be at from 7200 to 6500 F. At thistemperature there will be a very heavy asphaltic material re moved fromthese vapors which if allowed to remain in the tower 6 would eventuallyharden and plug the tower, hence we provide valve 18 through which aquantity of the heavy gas oil froml the bottom of #7 tower may beintroduced into tower 6. This heavy gas oil dissolves the asphalticmaterial removed from the vapors in tower 6 and carries it to the bottomof the tower where it is drawn ol by pump 12 as iiuel oil. The heavy gasoil introduced into this tower also serves as an added cooling mediumfor the incoming vapors and gives us a more flexible control over thetemperature of the gases leaving the tower. This tower 6 contains at itstop the heat exchanger 26, 26, 26 and 26 and in the bottom baille pansover which the heavy gas oil is made to flow to keep it asphalt-likematerial.

The temperature ot the vapors entering tower 7 should be approximatelyat the equilibrium boiling point of these vapors under the conditionsmaintained in that tower. At this temperature the quantity of heat to beremoved from these vapors is only that heat due to the condensation ofthe heavy gas oil we desire to remove in tower V7 and the heat we mustextract from the vapors themselves in order to cool the vapors to such atemperature that the heavy gas oil will liquify and drop out of thevapors; thereforethe heat exchanger at the top of this toweris smallerthan the heat exchanger in tower 6. In cooling the vapors in thisexchanger there is a certain quantity of lighter oils which will beabsorbed from the vapors by the condensing heavy gas oil. In order tothoroughly strip this heavy gas oil of these light oils we cause thesecondensed heavy gas oils to flow downward through the tower over aseries of bubble pans or the equivalent thereof in contact with thevapors entering this tower.

Tower 8 operates on the same general principles as tower 7, except thatit is used to remove the light gasoline absorbed from the vaporsentering tower ll, In this tower enough heat is taken from the vaporsenter ing it to cause the condensation oi a light oil and to cool thevapors until they are made up of only lixed gases and the desiredgasoline like vapors. .As the quantity of heat removed in this tower isless than the heat to be removed in the preceding towers, we have shownthe heat exchanger at the top of this tower with only one coil, 2S;Below this coil we have bubble pans 5l which serve to strip thecondensed light gas oil ot its absorbed gasoline and also to strip theabsorbA ing oil from tower ll of :its light gasoline by contacting thempreferably in counter-eurrent with the incoming vapors.

The vapors from tower 8 pass to water cooler 9 where they are brought toatmospheric temperature under which condition the gasoline like materialall condensed except t'or that entrained in the fixed gases. Thiscondensed liquid and the fixed gases are separated in drinn l0, thegasolinelike niaterial going to storage or any other place desired andthe fixed passing to tower ll where they are stripped of their entrainedlight gasoline by flowing counter current to a down flow of light gasoil removed from the bottom of tower 8 or. otherlightgas oil introducedfrom an outside source through valve 35.

The light gas oil from the bottom o'l" tower 8 is drawn through heatexchanger 17 by pump 15 where it loses its heat to cold oil drawn fromthe bottom of tower ll. This exchange of heat here cools the light gasoil from tower 8 to such an extent that it ncan be used in tower 11 andwhen it 1s introduced again into tower 8 very little added heat fromvapors entering tower 8 is necessary for the complete removal of thelight gasoline this oil has absorbed while passing through v tower 11.By this system of stripping the absorbing oil of its light gasolinecontent in the presence of the heavier gasoline vapors, we `get aproductA more stable under atmospheric conditions than is gasolineproduced in the ordinary way and having the light strippings from theabsorbing oil added to it afterwards. In other words, the absorbingtower 41l operating in connection with the tower 8, constitutes astabilizing system which also takes advantage of the heat a wailable inbottoms from tower 8, and uses the same to strip the absorbing oil ofits light gasoline content. y

That we claim is:

l. In a plant or' the class described a plurality ol serially connectedifractionating units containing serially connected heat exchangers, aplurality of means connected each to `one of said fractionators adaptedto withdraw condensateI therefrom, an outlet connection from each oisaid means to a eorrespending heat exchanger or preheating coil, in apreceding fractionator, and means to force condensate through said heatexchangers, whereby heavier and lighter condensate in succession may bedrawn oil and relluxed for retreatment the surfaces of said heatexchanging units increasing in size in proportion to the specii'icgravities of the several grades of condensate supplied thereto` andtherefore proportionately to the temperatures required to vaporize thesame.

2. In a plant of the class described, la plu rality of seriallyconnected fraetionating units containing serially connected heatexchangers, means connected to a plurality oli said iractionators asindividual units adapted to draw off and force condensate therefromthrough said heat exchangers, means for supplying cracked vapors to theiirst one of said fractionating units, means for partially condensingthe vapors in each unit and for passing unconde'nsed vapors to thenextunit, means for condensing an d separating the vapors from the lastunit, an absorption unit connected to said separatinov means and adaptedto receive fixed gases and entrained light gasoline therefrom, means forexposing the same in said absorption unit to contact with an absorbingoil, whereby said oil may strip oft the entrained light gasoline, meansto return said oii to the last unit of the fractionating system forrecovery of said light gasoline, and means for drawingoi'i1 condensatefrom the last unit of the fractionating system and forcing the saine inpart through said heat exchangers in the fractionators for reliuxcracking, and in partinto the upper portion of the absorption unit toact therein as absorbing oil.

WILLIS F. SIMS.-V VENUS U. OLDER.

